Starship Asterisk*

by **Chris Peterson** » Tue Jul 16, 2013 8:01 pm

neufer wrote:
You have exceptional eyesight and very dark clear skies :!:

I have pretty good corrected eyesight (although I know people with better astronomical acuity). And I do, indeed, have very dark skies, about as dark as they get.

I think the list of diffuse objects listed in the Wikipedia article is much too short. In fact, I've sat around at star parties with people trying for naked eye fuzzies, and with good knowledge of position and the use of averted vision, it's surprising how many objects can just be detected. There is no way that most of these would be observed casually or accidentally, however.

by **neufer** » Tue Jul 16, 2013 7:53 pm

Chris Peterson wrote:
neufer wrote:
Given a 85% lens transmittance M104 would have been a fuzzy magnitude 6.8 object in Galileo's 1" telescope.
No, it wouldn't. You can't manipulate or interpret the magnitude of extended objects the same way you do that of stars. I've observed M51 (mag 8.4) with my naked eye. M101 (mag 7.8) is difficult even in binoculars. M104 (mag 9) is easy in binoculars- I've even seen it in my wife's 8x22s. The apparent magnitude of galaxies isn't very useful at all in determining how visible they will be to the eye or through a telescope, since the magnitude is integrated over the extent of the objects, and fails to consider the intensity gradient. Galaxies like M104, which have bright cores, are much easier to see.

You have exceptional eyesight and very dark clear skies

http://en.wikipedia.org/wiki/Naked_eye wrote:
<<Theoretically, in a typical dark sky, the dark adapted human eye would see the about 5,600 stars brighter than +6m while in perfect dark sky conditions about 45,000 stars brighter than +8m might be visible.

The visibility of diffuse objects such as star clusters and galaxies is much more strongly affected by light pollution than the visibility of planets and stars. Under typical dark conditions only a few such objects are visible. These include the Pleiades, h/χ Persei, the Andromeda galaxy, the Carina Nebula, the Orion Nebula, Omega Centauri (magnitude 3.7), 47 Tucanae (magnitude 4.91) and the globular cluster M13 in Hercules (magnitude 5.2). The Triangulum Galaxy (M33) (magnitude 5.72) is a difficult averted vision object and only visible at all if it is higher than 50° in the sky. The globular clusters M 3 in Canes Venatici (magnitude 6.2) and M 92 in Hercules (magnitude 6.3) are also visble with the naked eye under such conditions.

Under really dark sky conditions, however, M33 (magnitude 5.72) is easy to see, even in direct vision. Many other Messier objects are also visible under such conditions. The most distant objects that have been seen by the naked eye are nearby bright galaxies such as Centaurus A (magnitude 6.84), Bode's Galaxy (magnitude 6.94), Sculptor Galaxy (magnitude 8), and Messier 83 (magnitude 7.54).

Five planets can be recognized as planets from earth with the naked eye: Mercury, Venus, Mars, Jupiter, and Saturn. Under typical dark sky conditions Uranus (magnitude +5.8) can be seen as well with averted vision. During daylight only the Moon and Sun are obvious naked eye objects, but in many cases Venus can be spotted in daylight and in rarer cases Jupiter. Close to sunset and sunrise bright stars like Sirius or even Canopus can be spotted with the naked eye as long as one knows the exact position in which to look.>>

by **Beyond** » Tue Jul 16, 2013 5:29 pm

by **emc** » Tue Jul 16, 2013 4:46 pm

If you live here, U R A NUS

by **Beyond** » Tue Jul 16, 2013 4:36 pm

All that inventing just to see a far away Uranus. Heck, they could have just used a mirror to see one close up.

by **Chris Peterson** » Tue Jul 16, 2013 4:34 pm

neufer wrote:Given a 85% lens transmittance M104 would have been a fuzzy magnitude 6.8 object in Galileo's 1" telescope.

No, it wouldn't. You can't manipulate or interpret the magnitude of extended objects the same way you do that of stars. I've observed M51 (mag 8.4) with my naked eye. M101 (mag 7.8) is difficult even in binoculars. M104 (mag 9) is easy in binoculars- I've even seen it in my wife's 8x22s. The apparent magnitude of galaxies isn't very useful at all in determining how visible they will be to the eye or through a telescope, since the magnitude is integrated over the extent of the objects, and fails to consider the intensity gradient. Galaxies like M104, which have bright cores, are much easier to see.

Mankind had thousands of years to observe a magnitude 5.32 Uranus with two good eyes but (apparently) they never did before the invention of the telescope.

I think it is very unlikely that Uranus went unobserved visually. It simply wasn't recognized as a planet- not surprising given its dimness and very slow apparent motion against the background stars.

by **neufer** » Tue Jul 16, 2013 1:00 pm

: [b][color=#0000FF]Flamsteed's Royal Greenwich Observatory mural arc with which he was first human to observe a magnitude 5.32 Uranus.[/color][/b]

Chris Peterson wrote:
A one inch aperture (especially at 5X) makes seeing the Sombrero very easy. While a larger aperture supports more magnification, which means more of the retina illuminated, that isn't necessary at all for simple detection of the object.

Given a 85% lens transmittance M104 would have been a fuzzy magnitude 6.8 object in Galileo's 1" telescope.

I have never heard of a magnitude 6.8 object being visible (easily or otherwise) with two good eyes much less one.

Mankind had thousands of years to observe a magnitude 5.32 Uranus with two good eyes but (apparently) they never did before the invention of the telescope.

http://en.wikipedia.org/wiki/John_Flamsteed wrote:
<<John Flamsteed FRS (19 August 1646 – 31 December 1719) was an English astronomer and the first Astronomer Royal. He was responsible for several of the earliest recorded sightings of the planet Uranus, which he mistook for a star and catalogued as '34 Tauri'. The first of these was in December 1690, which remains the earliest known sighting of Uranus by an astronomer.>>

by **Chris Peterson** » Tue Jul 16, 2013 3:21 am

neufer wrote:Why have a 5mm exit pupil on binoculars
if 5mm is the maximum eye dilation at night?

5-6 mm is pretty typical for adults. Of course, binoculars are largely intended for daytime use, and the makers don't want the objectives to be any larger than necessary (because of added weight and cost), so many binoculars are designed with a 5mm exit pupil. Astronomical binoculars are usually designed for a 7mm exit pupil, optimized for somewhat younger users with fully dilated pupils.

Twice the retina area means twice the number of illuminated rods & cones for each eye.

Indeed, and this does provide some benefit in sensitivity, even though the brightness is unchanged. It's one of the main reasons for using higher magnifications with dim objects.

4 air-glass surfaces => Transmission = (0.96)⁴ = 85%

Which is, in fact, barely noticeable.

Galileo had telescopes with effective apertures larger than an inch?

Not that I know of. A one inch aperture (especially at 5X) makes seeing the Sombrero very easy. While a larger aperture supports more magnification, which means more of the retina illuminated, that isn't necessary at all for simple detection of the object.

by **neufer** » Tue Jul 16, 2013 2:22 am

Chris Peterson wrote:
neufer wrote:
7 x 35 binoculars have almost 4 times the light gathering power of a 1" telescope
(especially a telescope with no anti-reflection coating).
Both have a 5mm exit pupil.

Why have a 5mm exit pupil on binoculars
if 5mm is the maximum eye dilation at night?

Chris Peterson wrote:
The 35mm aperture collects twice as much light,
but the higher power distributes it over twice the area of the retina, for no net increase in brightness.

Twice the retina area means twice the number of illuminated rods & cones for each eye.
(And, of course, binoculars mean twice that number of eyes.)

Chris Peterson wrote:
For a simple, two lens telescope like that used by Galileo, the improvement from AR coatings is minimal.

4 air-glass surfaces => Transmission = (0.96)⁴ = 85%

Chris Peterson wrote:
neufer wrote:In any event, the important point is that the APOD "suggests" that Galileo
was capable of observing M104 and we both agree that that is misleading.
I don't agree. There's no reason at all to think that Galileo couldn't have observed M104 with one of his lower power telescopes (3X or 8X), and possibly even with the 20X version he used on the planets. Some of the telescopes he had at his disposal were capable of making M104 readily visible. It's simply a problem of finding it.

Galileo had telescopes with effective apertures larger than an inch?

by **Chris Peterson** » Mon Jul 15, 2013 11:44 pm

neufer wrote:7 x 35 binoculars have almost 4 times the light gathering power of a 1" telescope
(especially a telescope with no anti-reflection coating).

Both have a 5mm exit pupil. The 35mm aperture collects twice as much light, but the higher power distributes it over twice the area of the retina, for no net increase in brightness. For a simple, two lens telescope like that used by Galileo, the improvement from AR coatings is minimal.

In any event, the important point is that the APOD "suggests" that Galileo
was capable of observing M104 and we both agree that that is misleading.

I don't agree. There's no reason at all to think that Galileo couldn't have observed M104 with one of his lower power telescopes (3X or 8X), and possibly even with the 20X version he used on the planets. Some of the telescopes he had at his disposal were capable of making M104 readily visible. It's simply a problem of finding it.

by **Anthony Barreiro** » Mon Jul 15, 2013 7:30 pm

This is a beautiful image!

Thanks Ann for the additional information about the Sombrero's odd shape and possible history.

The whole "small telescope" kerfuffle could have been avoided by linking to a picture of Pierre Mechain.

by **geckzilla** » Mon Jul 15, 2013 6:33 pm

You two are strangely and delightfully disagreeable when you are being agreeable.

by **neufer** » Mon Jul 15, 2013 6:03 pm

Chris Peterson wrote:
neufer wrote:
A fuzzy spread out magnitude 6.6 galaxy would be impossible to see, IMO.
It isn't hard to see the Sombrero through small binoculars.
You don't see much detail, but that it's a fuzzy oval is unmistakable.

7 x 35 binoculars have almost 4 times the light gathering power of a 1" telescope
(especially a telescope with no anti-reflection coating).

In any event, the important point is that the APOD "suggests" that Galileo
was capable of observing M104 and we both agree that that is misleading.

by **Chris Peterson** » Mon Jul 15, 2013 5:17 pm

neufer wrote:A night dilated pupil is about a third of an inch so make that 3X magnification.

That's large, even for a child. At Galileo's age when he was observing, his dilated pupil size would be about 5mm. With a 25mm aperture, he could reach 5X magnification before his view started to dim.

Hence, a magnitude 9 star would become a magnitude 6.6 star.

We aren't discussing stars. Detectable star brightness scales approximately as the area of the aperture. But that is not the case for extended objects, which are never brighter through a telescope than they are to the naked eye, and for which the brightness does not depend on aperture (except above a magnification threshold).

A fuzzy spread out magnitude 6.6 galaxy would be impossible to see, IMO.

It isn't hard to see the Sombrero through small binoculars. You don't see much detail, but that it's a fuzzy oval is unmistakable.

by **JohnD** » Mon Jul 15, 2013 5:16 pm

Quote, BDanielMayfield, "But, haven't you heard, The Ringworld is unstable!"

And that's why the Engineers installed the Rim Ramjets!

And if someone like Freeman Dyson can let down his supremely intellectual hair and indulge his imagination to think of Spheres, I can think of a Galactic RingWorld. Of course, I am thinking far too small, because as has been pointed out, a RingWorld is just a segment of a Sphere, and I should be imagining a Galactic Dyson Sphere!

But I think that has been done, and it would include an unbelievable volume of breathable air and such a low gradient gravity field, that beings could survive unsuited in permanent freefall, structures as big as planets could be built by Snartibartfast Inc., and you could get to Mars from Earth by flapping your wings and flying straight. Sort of Smoke Ring, without the navigational problem of "East takes you Out, Out takes you West, West takes you In, In takes you East. Port and Starboard bring you back."

John

by **neufer** » Mon Jul 15, 2013 4:59 pm

Chris Peterson wrote:
neufer wrote:Galileo's 1" refractor may have been fine for observing bright planets but it took another order of magnitude in light gathering power with Pierre Méchain's 3.5" refractor (170 years later) to observe the fuzzy Sombrero Galaxy.
A 1" aperture telescope will present views at a 5X magnification as bright as those through any telescope, of any larger size. At 5x, the Sombrero appears larger than the Moon. It can certainly be observed (and quite easily) using a good quality 1" telescope (which Galileo's was not). It didn't require a larger telescope, it's simply the case that the first person to observe this object was using a larger one (as were virtually all observers after Galileo).

A night dilated pupil is about a third of an inch so make that 3X magnification.

Hence, a magnitude 9 star would become a magnitude 6.6 star.

Few people could see a magnitude 6.6 star using both eyes much less using one
(although Galileo apparently could see a magnitude 5.6 planet).

A fuzzy spread out magnitude 6.6 galaxy would be impossible to see, IMO.

(A magnitude 9 star with Pierre Méchain's 3.5" refractor would become a magnitude 4.9 star.)

by **Chris Peterson** » Mon Jul 15, 2013 3:30 pm

neufer wrote:Galileo's 1" refractor may have been fine for observing bright planets but it took another order of magnitude in light gathering power with Pierre Méchain's 3.5" refractor (170 years later) to observe the fuzzy Sombrero Galaxy.

A 1" aperture telescope will present views at a 5X magnification as bright as those through any telescope, of any larger size. At 5x, the Sombrero appears larger than the Moon. It can certainly be observed (and quite easily) using a good quality 1" telescope (which Galileo's was not). It didn't require a larger telescope, it's simply the case that the first person to observe this object was using a larger one (as were virtually all observers after Galileo).

by **BDanielMayfield** » Mon Jul 15, 2013 2:16 pm

Thanks for that rapid response John.

A GALACTIC sized Ringworld??? The circumference of the Sombrero’s ring would be, what, about 380,000 lightyears. “The Ringworld” must have made a huge impression on you.

Bruce

P.S. I don't mean to imply that I'm laughting at you, but with you. I too thought that "The Ringworld" was a great story. But, haven't you heard, The Ringworld is unstable!

by **JohnD** » Mon Jul 15, 2013 1:51 pm

Like this,

Or this, our Sister Andromeda, from a link provided by the indefatigable neufer!

John

by **BDanielMayfield** » Mon Jul 15, 2013 1:47 pm

That was a very helpful reference Bystander.

I wonder, how might the Milky Way look from a similar distance and viewing angle?

by **JohnD** » Mon Jul 15, 2013 1:46 pm

Ok, Neufer, warm dust, cold dust, it "actually glows brightly in infrared light." http://apod.nasa.gov/apod/ap050511.html

Yes, it is sort of cold, >20K according to this paper: http://adsabs.harvard.edu/full/1995A%26A...303..673E which also offers several theories or mechanisms for the formation of the RingDust, that do not include a disintegrated Galactic RingWorld.

But I'd still like to ask. Banks descrobed the radial momentum of his Orbital as causing its residue to fly apart visibly. Would the same be true of the Galactic RingWorld if that were to disintegrate? Could we see it happening on this galactic scale and distance?

John

by **bystander** » Mon Jul 15, 2013 12:50 pm

Ann wrote:
http://www.universetoday.com/94800/spit ... es-in-one/ wrote:

Spitzer Spots Two Galaxies in One

http://asterisk.apod.com/viewtopic.php?t=28354

by **neufer** » Mon Jul 15, 2013 11:26 am

Click to play embedded YouTube video.

by **neufer** » Mon Jul 15, 2013 11:13 am

Click to play embedded YouTube video.

JohnD wrote:
I try not to fantasise about what APOD shows us. But an earlier InfraRed picture of the sombrero http://apod.nasa.gov/apod/ap050511.html shows that there is a complete ring of warm dust at the periphery of this galaxy, with little in the middle.

An earlier InfraRed picture of the sombrero http://apod.nasa.gov/apod/ap050511.html shows that there is a complete ring of cold dust at the periphery of this galaxy, with little cold dust in the middle.

by **neufer** » Mon Jul 15, 2013 11:04 am

RedFishBlueFish wrote:
How far away is this galaxy:
APOD says 50, Wiki says 30, and a YouTube clip put out by the Chandra telescope people
uses 25 million light years.

The 50 Mly probably comes from the average distance of the Virgo Cluster
of which the spiral M104 is a relatively near part.

http://en.wikipedia.org/wiki/Sombrero_Galaxy#Distance wrote:
<<At least two methods have been used to measure the distance to the Sombrero Galaxy.

The first method relies on comparing the measured fluxes from planetary nebulae in the Sombrero Galaxy to the known luminosities of planetary nebulae in the Milky Way. This method gave the distance to the Sombrero Galaxy as 29 ± 2 Mly.

The other method used is the surface brightness fluctuations method. This method uses the grainy appearance of the galaxy's bulge to estimate the distance to it. Nearby galaxy bulges will appear very grainy, while more distant bulges will appear smooth. Early measurements using this technique gave distances of 30.6 ± 1.3 Mly. Later, after some refinement of the technique, a distance of 32 ± 3 Mly was measured. This was even further refined in 2003 to be 29.6 ± 2.5 Mly.

The average distance measured through these two techniques is 29.3 ± 1.6 Mly.>>

Starship Asterisk*

APOD: The Sombrero Galaxy from Hale (2013 Jul 15)

Post a reply

Expand view Topic review: APOD: The Sombrero Galaxy from Hale (2013 Jul 15)

Re: APOD: The Sombrero Galaxy from Hale (2013 Jul 15)

Re: APOD: The Sombrero Galaxy from Hale (2013 Jul 15)

Re: APOD: The Sombrero Galaxy from Hale (2013 Jul 15)

Re: APOD: The Sombrero Galaxy from Hale (2013 Jul 15)

Re: APOD: The Sombrero Galaxy from Hale (2013 Jul 15)

Re: APOD: The Sombrero Galaxy from Hale (2013 Jul 15)

Re: APOD: The Sombrero Galaxy from Hale (2013 Jul 15)

Re: APOD: The Sombrero Galaxy from Hale (2013 Jul 15)

Re: APOD: The Sombrero Galaxy from Hale (2013 Jul 15)

Re: APOD: The Sombrero Galaxy from Hale (2013 Jul 15)

Re: APOD: The Sombrero Galaxy from Hale (2013 Jul 15)

Re: APOD: The Sombrero Galaxy from Hale (2013 Jul 15)

Re: APOD: The Sombrero Galaxy from Hale (2013 Jul 15)

Re: APOD: The Sombrero Galaxy from Hale (2013 Jul 15)

Re: APOD: The Sombrero Galaxy from Hale (2013 Jul 15)

Re: APOD: The Sombrero Galaxy from Hale (2013 Jul 15)

Re: APOD: The Sombrero Galaxy from Hale (2013 Jul 15)

Re: APOD: The Sombrero Galaxy from Hale (2013 Jul 15)

Re: APOD: The Sombrero Galaxy from Hale (2013 Jul 15)

Re: APOD: The Sombrero Galaxy from Hale (2013 Jul 15)

Re: APOD: The Sombrero Galaxy from Hale (2013 Jul 15)

Re: APOD: The Sombrero Galaxy from Hale (2013 Jul 15)

NGC 4594

Re: APOD: The Sombrero Galaxy from Hale (2013 Jul 15)

Re: Why not Disco Volante?